This invention relates to axial flow rotary combine harvesters and more particularly to the use of air to assist in the cleaning of threshed and separated grain.
The general arrangement of axial flow rotary combine harvesters in which, in an upper part of a separator housing, one or more fore-and-aft extending rotors are surrounded by an at least partially foraminous casing to provide the threshing and separating functions of the combine in their forward and rearward portions respectively is well known. Combine harvesters of this general type are disclosed in U.S. Pat. Nos. 3,827,443 Drayer and 3,645,270 Rowland-Hill. Typically, a cleaning shoe including reciprocating generally horizontal sieve elements is enclosed in a lower part of the separator housing and a grain pan and/or conveyor arrangement is provided to conduct separated grain, usually mixed with considerable chaff and other material other then grain (MOG), from the grates or concaves of the casing to the cleaning shoe. A blower provides air to assist in separating the chaff from the grain and act as a medium for carrying the separated chaff rearwardly from the cleaning shoe to be discharged through an opening in a rear wall of the separator housing.
It is characteristic of axial flow rotary threshing and separating devices to generate and deliver to the cleaning shoe, a greater proportion of chaff than is typical of the more conventional threshing and separating apparatus consisting of a transverse threshing cylinder and concave and reciprocating straw walkers. In addition, axial flow rotary threshing and separating devices have an inherently greater specific capacity than conventional machines so that if the capacity of te cleaning shoe is to match that of the separator and chaff overloading is to be avoided, it must be disproportionately large. U.S. Pat. No. 3,645,270 referred to above and U.S. Pat. Nos. 3,847,160 De Coene et al and 3,857,400 De Coene all disclose means intended to modify air flow in a separator housing, external to the separator or casing or concave, so as to improve cleaner efficiency but do not suggest means for reducing the amount of chaff entering the cleaning zone.